Red phosphor material and light-emitting device

ABSTRACT

A red phosphor material comprising an essential component represented by a formula of ALn 1-x-y Eu x Sm y M 2 O 8  as a main component, where A represents at least one selected from Li, Na, and K; Ln represents at least one selected from La and Gd; M represents at least one selected from W and Mo; and x and y are numerical values that satisfy 0.1≦x+y≦0.7 and 0.005≦y≦0.08. A light-emitting device includes an excitation light source and the red phosphor material that absorbs excitation light emitted by the excitation light source and emits red light.

BACKGROUND

1. Technical Field

The present disclosure relates to a red phosphor material that can beused for light-emitting devices such as light sources of projectors,light sources of vehicle-mounted head lamps, and light sources of whiteLED lighting apparatuses, the red phosphor material being used incombination with, for example, a light-emitting diode (LED) or asemiconductor laser diode (LD). The present disclosure also relates to alight-emitting device including the red phosphor material.

2. Description of the Related Art

Lighting apparatuses employing white LEDs have higher efficiency andlonger longevity than existing lighting apparatuses. From the standpointof resource savings and energy conservation, such lighting apparatuseshave come to be widely introduced for commercial use and home use.

Most commonly used white LEDs include a blue LED chip and a phosphorsubstance that partially absorbs blue light emitted by the LED chip andemits yellow light. This configuration causes mixing of blue light andits complementary-color light, that is, yellow light, resulting ingeneration of a pseudo-white color. There is ongoing development ofother white LEDs employing a combination of a blue LED chip, a greenphosphor substance, and a red phosphor substance in order to meetrequirements in terms of color rendering, color reproducibility, or thelike. There is also ongoing development of still other white LEDsemploying a combination of an LED chip emitting light in the nearultraviolet to blue violet region and three phosphor substances that area blue phosphor substance, a green phosphor substance, and a redphosphor substance.

For applications including light sources of projectors and light sourcesof vehicle-mounted head lamps, which require high emission energy, thereis ongoing development of light sources employing a combination of an LDemitting light in the near ultraviolet to blue violet region and aphosphor substance.

A known red phosphor substance that can be excited with light rangingfrom near-ultraviolet light to blue light is a phosphor substance thatis represented by the composition formula LiEuW₂O₈ and that emits lightin the red color region with Eu³⁺ serving as the luminescent center (forexample, refer to Japanese Unexamined Patent Application PublicationNos. 2003-41252, 2004-359842, 2005-255747, and 2009-260393). ThisLiEuW₂O₈ phosphor substance cannot be substantially excited with lasersor LED chips emitting light at 405 nm, which are readily available asexcitation light sources. However, it is known that a LiEuW₂O₈ phosphorsubstance in which Eu is partially substituted with Sm can be excitedwith lasers or LED chips emitting light at 405 nm (for example, refer toJapanese Unexamined Patent Application Publication No. 2004-359842).

SUMMARY

The inventors of the present disclosure have focused on the point thatred phosphor substances have been developed mainly with emphasis onlight-emitting efficiency and without performing studies on thetemperature characteristics of red phosphor substances. Althoughlight-emitting efficiency is an important characteristic, a relativelylow light-emitting efficiency can be compensated for by, for example,increasing the amount of phosphor substance used. In contrast, poortemperature characteristics cause problems: in particular, a lowluminance retention ratio at high temperature results in, in response tothe usage environment, variation in brightness or variation in colortone due to occurrence of disturbance in the balance between red lightand excitation light or light emitted by another phosphor substance. Inparticular, such problems markedly tend to occur in light-emittingdevices in which emission energy is high and the ambient temperature ofphosphor substances easily increases.

One non-limiting and exemplary embodiment provides a red phosphormaterial that has a high luminance retention ratio at high temperature.

In one general aspect, the techniques disclosed here feature a redphosphor material including an essential component represented by aformula of ALn_(1-x-y)Eu_(x)Sm_(y)M₂O₈ as a main component.

In the formula, A represents at least one selected from Li, Na, and K;Ln represents at least one selected from La and Gd; M represents atleast one selected from W and Mo; and x and y are numerical values thatsatisfy 0.1≦x+y≦0.7 and 0.005≦y≦0.08.

One non-limiting and exemplary embodiment can provide a red phosphormaterial that has a high luminance retention ratio at high temperature.

It should be noted that general or specific embodiments may beimplemented as a material, a device, an apparatus, a system, or amethod, or any selective combination thereof.

Additional benefits and advantages of the disclosed embodiments willbecome apparent from the specification and drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the emission spectrum of a red phosphor materialaccording to an embodiment of the present disclosure;

FIG. 2 illustrates the excitation spectrum of a red phosphor materialaccording to an embodiment of the present disclosure; and

FIG. 3 illustrates the measurement temperature dependency of theluminance of a red phosphor material according to an embodiment of thepresent disclosure.

DETAILED DESCRIPTION

Hereinafter, the present disclosure will be described in detail withreference to specific embodiments. However, the present disclosure isnot limited to these embodiments and modifications may be appropriatelymade without departing from the spirit and scope of the presentdisclosure.

A red phosphor material according to the present disclosure includes anessential component represented by a formula ofALn_(1-x-y)Eu_(x)Sm_(y)M₂O₈. This essential component serves as the maincomponent of the red phosphor material. In this specification, the term“main component” denotes a component that accounts for 70% by weight ormore of the red phosphor material, desirably 90% by weight or more, moredesirably 95% by weight or more, still more desirably 98% by weight ormore.

In the formula, A represents at least one selected from Li, Na, and K.From the standpoint of light-emitting efficiency, A desirably includesat least one selected from Li and Na, more desirably represents at leastone selected from Li and Na, and, in particular, desirably representsLi.

Ln represents at least one selected from La and Gd. From the standpointof luminance retention ratio at high temperature, Ln desirably includesGd, more desirably represents Gd.

M represents at least one selected from W and Mo. From the standpoint ofluminance retention ratio, M desirably includes W, more desirablyrepresents W.

In the formula, x and y are numerical values that satisfy 0.1≦x+y≦0.7and 0.005≦y≦0.08. From the standpoint of light-emitting efficiency, xand y desirably satisfy 0.2≦x+y≦0.7.

When a red phosphor material is produced such that x and y satisfy0.2≦x+y≦0.7 and 0.005≦y≦0.08, this red phosphor material is easilyexcited with light at a wavelength of 405 nm and has a high luminanceretention ratio at high temperature.

An embodiment of the present disclosure can provide a red phosphormaterial that is easily excited with light at a wavelength of 405 nm andhas a high luminance retention ratio at high temperature. This phosphormaterial can be excited with readily available excitation light sourcesthat are lasers or LED chips emitting light at a wavelength of 405 nm,which is highly advantageous in practical use. Another embodiment of thepresent disclosure can provide a light-emitting device in which, even athigh temperature, a decrease in brightness and variation in color tonedue to a decrease in the luminance of the red phosphor material tend notto occur.

When a red phosphor material according to an embodiment of the presentdisclosure is produced so as to have an emission wavelength of 615 nm, ameasured excitation spectrum for the red phosphor material has a peak ata wavelength of 405 nm. It is not necessary that this peak wavelength bestrictly 405 nm. For example, the peak wavelength may shift from 405 nmby about ±3 nm. The peak at a wavelength of 405 nm desirably has a peakintensity that is 30% or more, in particular, 40% or more of the peakintensity of the maximum peak in the wavelength region of 350 to 500 nm.

In a red phosphor material according to an embodiment of the presentdisclosure, a ratio of a luminance of emitted light as a result ofexcitation with light having a wavelength of 405 nm at 200° C. to aluminance of emitted light as a result of excitation with light having awavelength of 405 nm at 30° C. is 80% or more, desirably 85% or more.The luminance retention ratio can be measured by a method that will bedescribed in detail in EXAMPLES below.

As described above, x and y desirably satisfy 0.2≦x+y≦0.7. In a casewhere x+y is less than 0.2, the light-emitting efficiency relativelydecreases. In a case where x+y is more than 0.7, the luminance retentionratio decreases. As described above, y satisfies the range of0.005≦y≦0.08. In a case where y is less than 0.005, excitation cannot besubstantially achieved with light at 405 nm. In a case where y is morethan 0.08, both of the light-emitting efficiency and the luminanceretention ratio decrease.

In the formula, x and y desirably satisfy 0.2≦x+y≦0.6 and y moredesirably satisfies 0.005≦y≦0.04. In a case where x and y satisfy theseranges, it is easy to achieve a luminance retention ratio of 85% or morein the range of 30° C. to 200° C.

A red phosphor material according to an embodiment of the presentdisclosure may contain, in addition to the essential component, adesired component. This desired component is desirably at least oneselected from Li₂O, Na₂O, K₂O, CaCl₂, SrCl₂, BaCl₂, and B₂O₃. Hereafterthis desired component will be referred to as an addition component.

The content of the addition component relative to the entirety of thered phosphor material is desirably 0.05% to 2.0% by weight. This contentof the addition component may be adjusted, in accordance with, forexample, the composition of the essential component, to be in the rangeof 0.1% to 2.0% by weight, in the range of 0.1% to 1.0% by weight, ifnecessary, in the range of 0.15% to 1.0% by weight.

A red phosphor material according to an embodiment of the presentdisclosure consists essentially of the essential component and theaddition component. A red phosphor material according to anotherembodiment of the present disclosure consists essentially of theessential component. In this specification, “consists essentially of”means that the content of such a component or components relative to theentirety of the material is 99% by weight or more, desirably 99.5% byweight or more, more desirably 99.9% by weight or more. The term“essentially” is intended to permit the presence of trace componentsrepresented by impurities unavoidably introduced from raw materials orthe like.

A red phosphor material according to an embodiment of the presentdisclosure is a sinter. The sinter can be obtained by sintering powderraw materials. In this case where the red phosphor material is a sinter,effects caused by light scattering are reduced and the absorption ratioof excitation light increases, resulting in an increase inlight-emitting efficiency. In a case where the sinter is provided so asto have a small sample thickness, excitation light can be partiallypassed through the sinter. In another case, excitation light may be usedso as to be reflected by the sinter.

The sinter desirably has a density of 5.0 g/cm³ or more, more desirably5.5 g/cm³ or more. By increasing the density, the light-emittingefficiency can be sufficiently increased and light transmittance can beincreased.

The addition component exerts an effect of promoting densification of asinter. This effect results in a further increase in the light-emittingefficiency. Accordingly, in a case of providing a sinter, it isparticularly desirable to use the addition component. Note that B₂O₃ isnot expected to exert the effect of promoting densification. From thisstandpoint, a desired addition component is at least one selected fromLi₂O, CaCl₂, and SrCl₂.

The red phosphor material may contain a small amount of an auxiliarycomponent other than the addition component. This auxiliary componentmay be, for example, a component in which at least a part of theelements of the formula of the essential component serving as a maincomponent is substituted with an element other than the elements definedin the formula. For example, A may be substituted with Rb or Cs; and Lnmay be substituted with Y or Lu. Even when the red phosphor materialcontains such an auxiliary component, the main component of the materialis the above-described essential component.

The red phosphor material may be produced by any of a solid-phasemethod, a liquid-phase method, and a gas-phase method. In thesolid-phase method, raw material powders containing metals (for example,metal oxides or metal carbonates) are mixed and heat-treated at apredetermined temperature to cause a reaction. In the liquid-phasemethod, a solution containing metals is prepared; and a solid phase isobtained by precipitating the solid phase from this solution or byapplying the solution onto a substrate and subsequently subjecting thesolution to drying and a heat treatment at a predetermined temperatureor the like. In the gas-phase method, vapor deposition, sputtering, CVD,or the like is carried out to provide a film-shaped solid phase. Amongthese methods, the solid-phase method is desirable because it can becarried out at low cost and is suitable as a method of providing asinter.

The raw materials used in the solid-phase method may be commonly usedraw material powders of oxides, carbonates, or the like. In thesolid-phase method, such raw material powders are mixed with, forexample, a ball mill to prepare a powder mixture; this powder mixture isheat-treated with, for example, a normal electric furnace to therebyprovide a phosphor material. The atmosphere during the heat treatmentmay be an inert gas atmosphere such as N₂ gas. Alternatively, the heattreatment may be carried out in the air because Eu³⁺ emits light in ared phosphor material according to this embodiment.

In a case of producing a sinter, a powder mixture of raw materials maybe heat-treated to prepare a phosphor powder and this powder may besubsequently sintered. However, use of such a production method mayresult in a low degree of sintering and the resultant sinter tends notto have a high density. For this reason, a powder mixture of rawmaterials is desirably heat-treated to thereby be sintered. In otherwords, without carrying out a preliminary heat treatment for preparing aphosphor substance, a single heat treatment is desirably carried out tothereby achieve synthesis and sintering of a phosphor substance. A redphosphor material according to this embodiment is desirably obtained bya heat treatment during which synthesis and sintering of the phosphorsubstance proceed simultaneously. In this case, prior to the heattreatment, the powder mixture of raw materials may be shaped so as tohave a predetermined shape. This shaping may be appropriately performedby a sheet forming process or the like. Alternatively, a commonly usedmolding process may be employed.

In a case of producing a sinter from a powder prepared as a phosphorsubstance, a powder of raw materials, desirably not containing anyaddition component that is at least one selected from Li₂O, CaCl₂, andSrCl₂, is heat-treated to prepare a phosphor powder; this phosphorpowder is mixed with the addition component, shaped, and heat-treated tobe sintered. In this way, a low sinter density can be avoided.

A red phosphor material according to an embodiment of the presentdisclosure is an oxide material. Thus, the heat treatment can be carriedout in the air and hence the material can be produced easily at lowcost.

A red phosphor material according to an embodiment of the presentdisclosure can be excited with light having a wavelength in the nearultraviolet to blue region, in particular, 405 nm; the phosphor materialemits light at about 615 nm, which is highly visible; and the phosphormaterial has a good temperature characteristic, specifically, aluminance retention ratio. In addition, the luminance tends not todecrease even in a case of using a high-power excitation source such asa laser diode. A phosphor substance having a short afterglow period (forexample, 1/10 afterglow for about 1 msec) for Eu³⁺ phosphor substancescan also be provided.

According to an embodiment of the present disclosure, a red phosphormaterial with substantially no variation in emission spectrum inresponse to temperature can also be provided. In this case, theluminance retention ratio and a photon number retention ratio aresubstantially the same.

A light-emitting device including a red phosphor material according tothe present disclosure includes an excitation light source. The redphosphor material partially absorbs excitation light emitted by theexcitation light source and emits red light. Alternatively, such alight-emitting device may include no excitation light source. Examplesof the light-emitting device include various light sources employing alight-emitting diode (LED) and/or a semiconductor laser diode (LD) and aphosphor substance, such as light sources of projectors, light sourcesof vehicle-mounted head lamps, and light sources of white LED lightingapparatuses.

Such a light-emitting device includes, as an excitation light source,for example, a semiconductor light-emitting element that emits lighthaving a peak wavelength in the wavelength range of 380 to 470 nm. Thesemiconductor light-emitting element has a light-emitting layer formedof, for example, a gallium nitride compound semiconductor.

A red phosphor material according to an embodiment of the presentdisclosure has spectrum peaks for excitation at wavelengths of about 385nm, about 396 nm, about 405 nm, about 420 nm, and about 465 nm. Thus,the excitation light source such as a semiconductor light-emittingelement desirably has an emission wavelength that is close to one ofthese wavelengths. A spectrum peak for excitation at a wavelength ofabout 405 nm appears in a red phosphor material containing Sm.

A light-emitting device according to an embodiment of the presentdisclosure is a white LED. This white LED is not particularly limited interms of configuration or production method. For example, the white LEDcan be produced in the same manner as in existing white LEDs except thatexisting red phosphor materials are replaced by a red phosphor materialaccording to an embodiment of the present disclosure.

EXAMPLES

Hereinafter, the present disclosure will be described further in detailwith reference to Examples and Comparative examples. However, thepresent disclosure is not limited to the following Examples.

Example 1

The starting materials used were Li₂CO₃, La₂O₃, Eu₂O₃, Sm₂O₃, and WO₃powders of the guaranteed reagent grade or higher. The predeterminedamounts of these raw materials were weighed and prepared. These rawmaterial powders were wet-blended with pure water as a medium in a ballmill, and dried at 130° C. to provide a powder mixture. Subsequently,this powder mixture was fired at 850° C. in the air for 2 hours toprovide a phosphor powder that was not a sinter.

The above-described raw materials were added such that atomicproportions of Li, La, Eu, Sm, and W satisfied values in Table 1. Inparticular, Li₂CO₃ was excessively added: the amount of Li₂CO₃ added wasconverted in terms of oxide into an amount (weight) of Li₂O; an excessamount (weight) of Li₂O was determined by subtracting, from this amount,a required amount of Li₂O stoichiometrically determined on the basis ofthe formula of the essential component; and the ratio of this excessamount to the entirety of the red phosphor material was 0.3%.

Such obtained phosphor powders were measured with a fluorescencespectrometer FP-6500 (light source: xenon lamp) manufactured by JASCOCorporation in terms of emission spectrum in the range of 550 nm to 750nm with excitation light at a wavelength of 396 nm. In addition, thephosphor powders were measured at an emission wavelength of 615 nm interms of excitation spectrum in the range of 350 nm to 500 nm.

The No. 2 phosphor powder was also measured in terms of luminanceretention ratio in the range of 30° C. to 200° C. with the fluorescencespectrometer with excitation light at a wavelength of 405 nm. Theluminance retention ratio was determined in the following manner: atmeasurement temperatures, the luminance of light emitted by the phosphorpowder in the wavelength range of 550 to 750 nm was measured withexcitation light at a wavelength of 405 nm; and the ratio of theluminance of emitted light at 200° C. to the luminance of emitted lightat 30° C. (the luminance retention ratio in the range of 30° C. to 200°C.) was calculated. In this measurement, the temperature of theatmosphere was sequentially increased to 30° C., 50° C., 150° C., and to200° C.; and the luminance of emitted light was measured at each ofthese temperatures.

The results are illustrated in FIGS. 1 to 3.

Referring to FIG. 1, Sample Nos. 1 and 2 exhibited very similar emissionspectra and were found to be red phosphor materials that emit lighthaving a main peak at 615 nm. The red phosphor materials of Sample Nos.1 and 2 are useful as red phosphor materials used with excitation lightat a wavelength of 396 nm.

Referring to FIG. 2, Sample No. 1, which contained no Sm, had excitationspectrum peaks at about 385 nm, about 396 nm, about 420 nm, and about465 nm. This means that Sample No. 1 can be excited with light rangingfrom near-ultraviolet light to blue light. Sample No. 2, which containedSm, had, in addition to these peaks, another excitation spectrum peak atabout 405 nm. Introduction of Sm allows excitation even with readilyavailable LED chips or semiconductor lasers that emit light at 405 nm.

Referring to FIG. 3, the Sample No. 2 phosphor material had goodluminance retention ratios relative to the luminance at 30° C.: 90.2% at150° C., and 83.7% at 200° C.

TABLE 1 Addition Essential component (atomic proportions) component No.A Ln Eu Sm M (wt %) 1 Li = 1.0 La = 0.7 0.30 0 W = 2.0 Li₂O = 0.3 2 Li =1.0 La = 0.7 0.28 0.02 W = 2.0 Li₂O = 0.3

Example 2

Powder mixtures having composition proportions in Nos. 5 to 35 in Table2 were prepared as in Example 1 except that raw materials not describedin Example 1 were additionally used: oxides, carbonates, and the like ofthe guaranteed reagent grade or higher (Gd₂O₃, Y₂O₃, MoO₃, Na₂CO₃,K₂CO₃, CaCl₂, SrCl₂, and BaCl₂). These powders were compacted with moldshaving a diameter of 20 mm. The resultant compacts were fired at 800° C.to 1000° C. for 2 hours in the air. Thus, sintered samples having adiameter of about 14 mm and a thickness of about 1 mm were obtained.

These sinters were measured in terms of luminance retention ratio in therange of 30° C. to 200° C. as in Example 1. In addition, an absolute PLquantum yields measurement system Model C9920 manufactured by HamamatsuPhotonics K. K. was used to measure, at an excitation wavelength of 405nm, internal quantum efficiency (IQE), excitation light absorbance(Abs.), and the product of IQE and Abs., external quantum efficiency(EQE).

In addition, the Sample Nos. 1 and 2 phosphor powders produced inExample 1 were compacted and, without being fired, measured in the samemanner as above. These samples were defined as Sample Nos. 1 and 2 inExample 2. In addition, sintered samples having the same compositions asSample Nos. 1 and 2 in Example 1 were produced in the same manner asabove. These samples were defined as Sample Nos. 3 and 4 in Example 2.These samples were also evaluated in the same manner as above. Theresults are summarized in Table 2.

TABLE 2 Essential component (atomic proportions) Addition Light-emittingefficiency (%; 405 nm) Retention No A Ln Eu Sm M component (wt %) IQEAbs. EQE ratio (%)  1 Li = 1.0 La = 0.7 0.30 0 W = 2.0 Li₂O = 0.3 29.322.9 6.7 102.2  2 Li = 1.0 La = 0.7 0.28 0.02 W = 2.0 Li₂O = 0.3 62.643.6 27.3 83.7  3 Li = 1.0 La = 0.7 0.30 0 W = 2.0 Li₂O = 0.3 30.8 28.88.9 103.8  4 Li = 1.0 La = 0.7 0.28 0.02 W = 2.0 Li₂O = 0.3 68.4 63.843.6 84.9  5 Li = 1.0 Gd = 0.9 0.08 0.02 W = 2.0 Li₂O = 0.3 47.5 55.726.5 88.9  6 Li = 1.0 Gd = 0.8 0.18 0.02 W = 2.0 Li₂O = 0.3 66.6 60.240.1 88.7  7 Li = 1.0 Gd = 0.7 0.28 0.02 W = 2.0 Li₂O = 0.3 69.2 64.944.9 88.3  8 Li = 1.0 Gd = 0.5 0.48 0.02 W = 2.0 Li₂O = 0.3 75.9 63.648.3 86.9  9 Li = 1.0 Gd = 0.3 0.68 0.02 W = 2.0 Li₂O = 0.3 68.2 65.444.6 81.1  10* Li = 1.0 Gd = 0.2 0.78 0.02 W = 2.0 Li₂O = 0.3 59.6 67.840.4 76.5  11* Li = 1.0 — 0.98 0.02 W = 2.0 Li₂O = 0.3 56.3 69.5 39.174.5 12 Li = 1.0 Gd = 0.7 0.30 0 W = 2.0 Li₂O = 0.3 40.4 32.6 13.2 106.513 Li = 1.0 Gd = 0.7 0.295 0.005 W = 2.0 Li₂O = 0.3 64.7 53.8 34.8 89.814 Li = 1.0 Gd = 0.7 0.26 0.04 W = 2.0 Li₂O = 0.3 65.6 66.9 43.9 85.7 15Li = 1.0 Gd = 0.7 0.24 0.06 W = 2.0 Li₂O = 0.3 62.0 67.3 41.7 83.5 16 Li= 1.0 Gd = 0.7 0.22 0.08 W = 2.0 Li₂O = 0.3 51.3 72.1 37.0 81.4  17* Li= 1.0 Gd = 0.7 0.2 0.1 W = 2.0 Li₂O = 0.3 41.5 73.3 30.4 78.3 18 Na =1.0 Gd = 0.7 0.28 0.02 W = 2.0 Na₂O = 0.3 62.4 61.1 38.1 84.6 19  K =1.0 Gd = 0.7 0.28 0.02 W = 2.0 K₂O = 0.3 60.1 57.9 34.8 82.9  20* Li =1.0  Y = 0.7 0.28 0.02 W = 2.0 Li₂O = 0.3 56.9 64.8 36.9 79.0 21 Li =1.0 Gd = 0.7 0.28 0.02 Mo = 2.0  Li₂O = 0.3 68.9 63.0 43.4 82.2 22 Li =1.0 Gd = 0.7 0.28 0.02 W = 2.0 — 57.3 60.8 34.8 84.3 23 Li = 1.0 Gd =0.7 0.28 0.02 W = 2.0 Li₂O = 0.05 58.7 61.0 35.8 85.6 24 Li = 1.0 Gd =0.7 0.28 0.02 W = 2.0 Li₂O = 0.1 64.2 63.1 40.5 87.4 25 Li = 1.0 Gd =0.7 0.28 0.02 W = 2.0 Li₂O = 0.5 65.4 65.7 43.0 88.0 26 Li = 1.0 Gd =0.7 0.28 0.02 W = 2.0 Li₂O = 1.0 55.5 66.0 36.6 86.2 27 Li = 1.0 Gd =0.7 0.28 0.02 W = 2.0 Li₂O = 2.0 54.7 52.8 28.9 83.1 28 Li = 1.0 Gd =0.7 0.28 0.02 W = 2.0 CaCl₂ = 0.05 58.1 61.6 35.8 84.7 29 Li = 1.0 Gd =0.7 0.28 0.02 W = 2.0 CaCl₂ = 0.1 62.7 62.0 38.9 85.9 30 Li = 1.0 Gd =0.7 0.28 0.02 W = 2.0 CaCl₂ = 0.5 69.9 64.4 45.0 87.9 31 Li = 1.0 Gd =0.7 0.28 0.02 W = 2.0 CaCl₂ = 1.0 68.5 64.8 44.4 87.7 32 Li = 1.0 Gd =0.7 0.28 0.02 W = 2.0 CaCl₂ = 2.0 54.0 60.5 32.7 84.8 33 Li = 1.0 Gd =0.7 0.28 0.02 W = 2.0 SrCl₂ = 0.5 69.8 64.2 44.8 87.5 34 Li = 1.0 Gd =0.7 0.28 0.02 W = 2.0 BaCl₂ = 0.5 69.2 62.3 43.1 85.0 35 Li = 1.0 Gd =0.7 0.28 0.02 W = 2.0 B₂O₃ = 0.5 67.9 59.9 40.7 84.0 Samples marked with*: Comparative examples, Retention ratio: luminance retention ratio inthe range of 30° C. to 200° C., Content of addition component: ratio ofaddition component to the entirety of the phosphor material

The measurements in Example 2 were carried out with excitation light at405 nm. Accordingly, Nos. 1 and 3 not containing Sm have a low Abs.,which results in a low EQE. In contrast, Nos. 2 and 4 containing Sm havea high Abs. and a high EQE. Comparison between Nos. 1 and 3 andcomparison between Nos. 2 and 4 indicate that formation as a sinterresults in an increase in Abs. and an increase in EQE.

Table 2 indicates the following. A red phosphor material that is excitedwith light having a wavelength of 405 nm desirably contains Sm such thaty in the formula of the essential component is 0.005 or more. Redphosphor materials that contained Sm and were excited with light havinga wavelength of 405 nm exhibited an EQE of 20% or more. Note that, byusing excitation light having another wavelength (for example, awavelength of 396 nm used in Example 1), red phosphor materials whoseessential component contains no Sm (y=0) can also exhibit good emissionproperties.

Nos. 5 to 17 indicate results of cases where the Eu proportion (x) andthe Sm proportion (y) were varied. In Nos. 5 to 11, a case in which the“Eu+Sm” proportion (x+y) was low also exhibited a luminance retentionratio of more than 80%. However, in spite of containing Sm, this caseexhibited an EQE of less than 30%. In Nos. 5 to 11, other cases in whichthe proportion (x+y) was excessively high exhibited a luminanceretention ratio of less than 80%. In Nos. 7 and 12 to 17, a case inwhich the Sm proportion (y) was low exhibited a luminance retentionratio of more than 80%. However, this case exhibited a low EQE withexcitation at 405 nm. In Nos. 7 and 12 to 17, a case in which the Smproportion (y) was excessively high exhibited a luminance retentionratio of less than 80%.

Nos. 7, 18, and 19 indicate the following. Any of Li, Na, and K isusable as the alkali metal element (A). However, use of Na or K resultsin a much lower EQE than that provided by use of Li. Accordingly, theelement A is most desirably Li.

Nos. 4, 7, and 20 indicate the following. Use of Y as the rare earthelement (Ln) causes a decrease in the luminance retention ratio to lessthan 80%. Use of La or Gd provides a higher luminance retention ratiothan that provided by use of Y. Use of Gd results in a higher EQE and ahigher luminance retention ratio. Accordingly, the element Ln is mostdesirably Gd.

Nos. 7 and 21 indicate the following. Instead of W, Mo can be used.However, use of W results in an increase in the luminance retentionratio. Accordingly, the element M is desirably W.

Comparison between No. 22 containing no addition component and Nos. 7,23 to 27, and 28 to 32 containing an addition component of Li₂O or CaCl₂indicates the following. Addition of an addition component results in anincrease in IQE and an increase in Abs. As a result, EQE is alsoincreased and the luminance retention ratio is also increased. Theeffect provided by addition of an addition component is markedlyachieved when the amount of the addition component is in the range of0.1% to 1.0% by weight. An improvement in Abs. due to addition of Li₂Oor CaCl₂ was markedly achieved for phosphor materials that were sinters.This is probably because addition of the addition component resulted inan increase in the density of the sinters.

Nos. 33, 34, and 35 indicate results of cases of using SrCl₂, BaCl₂, orB₂O₃ as an additive. Addition of SrCl₂ provided an effect similar tothat provided by Li₂O or CaCl₂. This effect was slightly weaker in thecase of adding BaCl₂, and further weaker in the case of adding B₂O₃.Addition of B₂O₃ resulted in an increase in IQE; however, Abs. was notincreased and the effect of promoting densification of a sinter was notobserved. Accordingly, desired additives are Li₂O, CaCl₂, SrCl₂, andBaCl₂; in particular, desired additives are Li₂O, CaCl₂, and SrCl₂.

Similarly, the inventors of the present disclosure carried outexperiments in terms of other various compositions. As a result, theinventors have confirmed that red phosphor materials within the scope ofthe present disclosure have excellent properties as in theabove-described Examples.

Example 3

The No. 2 powder in Example 1 was prepared and added in a ratio of 10%by weight to a dimethyl silicone resin. The resultant mixture waskneaded with a three-roll kneader to provide an uncured phosphor resinmixture.

Subsequently, an LED chip that emits light having a central wavelengthof 405 nm was prepared. This LED chip was covered with the phosphorresin mixture and heated to cure the resin. Thus, an LED device wasproduced. Current was passed through the LED chip to cause lightemission. It was confirmed that red light was observed.

A red phosphor material according to the present disclosure is usefulfor various applications. Specifically, for example, the red phosphormaterial can be used for a light-emitting diode (LED). The red phosphormaterial can also be used for various light sources such as lightsources of vehicle-mounted head lamps, light sources of white LEDlighting apparatuses, and light sources of projectors employing asemiconductor laser diode (LD) and a phosphor substance.

What is claimed is:
 1. A red phosphor material comprising an essentialcomponent represented by a formula of ALn_(1-x-y)Eu_(x)Sm_(y)M₂O₈ as amain component, where A represents at least one selected from Li, Na,and K; Ln represents at least one selected from La and Gd; M representsat least one selected from W and Mo; and x and y are numerical valuesthat satisfy 0.1≦x+y≦0.7 and 0.005≦y≦0.08.
 2. The red phosphor materialaccording to claim 1, wherein x and y satisfy 0.2≦x+y≦0.7.
 3. The redphosphor material according to claim 1, wherein x and y satisfy0.2≦x+y≦0.6 and 0.005≦y≦0.04.
 4. The red phosphor material according toclaim 1, further comprising, in addition to the essential component, anaddition component that is at least one selected from Li₂O, Na₂O, K₂O,CaCl₂, SrCl₂, BaCl₂, and B₂O₃, wherein a content of the additioncomponent relative to an entirety of the red phosphor material is 0.05%to 2.0% by weight.
 5. The red phosphor material according to claim 4,consisting essentially of the essential component and the additioncomponent.
 6. The red phosphor material according to claim 4, being asinter.
 7. The red phosphor material according to claim 1, consistingessentially of the essential component.
 8. The red phosphor materialaccording to claim 1, wherein Ln represents Gd.
 9. The red phosphormaterial according to claim 1, wherein M represents W.
 10. The redphosphor material according to claim 1, wherein A represents at leastone selected from Li and Na.
 11. The red phosphor material according toclaim 1, wherein a ratio of a luminance of emitted light at a wavelengthof 615 nm as a result of excitation with light having a wavelength of405 nm at 200° C. to a luminance of emitted light at a wavelength of 615nm as a result of excitation with light having a wavelength of 405 nm at30° C. is 80% or more.
 12. A light-emitting device comprising anexcitation light source and a red phosphor material that absorbsexcitation light emitted by the excitation light source and emits redlight, the red phosphor material comprising an essential componentrepresented by a formula of ALn_(1-x-y)Eu_(x)Sm_(y)M₂O₈ as a maincomponent, where A represents at least one selected from Li, Na, and K;Ln represents at least one selected from La and Gd; M represents atleast one selected from W and Mo; and x and y are numerical values thatsatisfy 0.1≦x+y≦0.7 and 0.005≦y≦0.08.